Re: Do monsters in hell mode drop good items better if the game is full?
Few exceptions:
Countess will drop el through ist more with less players (mf has no impact) but Gul through Lo more with more players. (Chances of Gul-Lo are only a very small fraction of ist, however, so not worth it).
Superuniques except those baal summons (which drop like if they're champions) always drop 2 items and 4 potions, more or less players have no impact, only MF and monster level.
Random uniques always drop one item and 4 potions, more or less players have no impact, only MF and monster level.
Griswold and The Smith drop base items in NM as if they were in hell, but have too low monster level to drop the higher level uniques. Sets, however, are a different story. These two bosses are the only ones I know of that can drop white items; you may even get your eth superior Colossos Voulge from one of them (!). Griswold IIRC is incorrectly robbed of his +3 monster level in ATMA, so he's mlvl 87 in hell, and thus can drop Arachnid's Mesh. Bosses like these, the smith, summoner, etc, DO have a nodrop possibility, so the more players, the more they drop.
Champions always drop two potions, and one item/gold pile. Only monster level and MF/GF count.
Act bosses also have a nodrop, but due to the 6 items per drop hard cap, they max out their drop at 5 or even 3 players (unpartied).
In 1.09 (and possibly later/earlier patches) act bosses seemed to be able to drop more than 6 items, but it was discovered that for some reason their gold drop created several piles. I don't know if the reason was ever uncovered.
Probably too much info, but you only need to bother about the parts that you find interesting and/or useful
EDIT: Oh, and sometimes the game tries to drop items on unpassable terrain (like space in arcane sanctuary). In that case, the items are lost. I do not know if a unique is flagged as "dropped" in that game if it is attempted to drop over unpassable terrain, but someone with modding skills could easily test this.
Fangskin in hell drops nothing, due to a bug introduced in 1.11. My little conspiracy theory is that someone wanted to nerf pindleskin runs, but got the names mixed up.